Elementary Particles

2. WHO IS THIS ARTICLE FOR?

Particle physics is the branch of physics aimed at understanding the structures and interactions of the smallest particles that exist in an atom and understanding the forces that act between them.

Surprisingly, the study of the smallest known objects has a number of striking shared features with the study of our universe at large.

Everything in the universe is made of some fundamental particles that are governed by four fundamental forces. Our understanding of the fundamental particles is encapsulated in the Standard Model of particle physics, developed in the early 1970s. Since then, the Standard Model has successfully explained almost all experimental results and precisely predicted a wide variety of phenomena. Over time it has become a well-tested theory verified by many experiments.

Although the Standard Model is extremely successful as a mathematical model for describing the interactions of all particles known to us, it is by no means complete. None of the particles of the Standard Model can account for dark matter that makes up for most of the matter in the universe. Scientists have known about a dark matter from the 1930s. It is the additional source of gravity that cannot be attributed to the things we can see, like stars and nebulae. Every galaxy has invisible halos of dark matter which keeps the stars from flying apart. Scientists have realized dark matter is an unknown form of matter, made up of an unknown elementary particle.

Now is a very exciting time for particle physics especially because the LHC has recently undergone a major upgrade. It is now capable of accelerating particles to a record energy of 13 TeV — an energy regime unexplored so far. Collisions at this energy can open up a slew of phenomena never seen before. Scientists are hoping to find out if supersymmetry, the theory that fills some gaps in the Standard Model is a viable theory or just a mathematical concoction. Among other things, supersymmetry can explain the mass of the Higgs boson itself (Standard Model cannot) and can provide a basis to unify nature’s forces. LHC may also be able to indicate if dark matter is a supersymmetric particle or something completely new.

The language of particle physics is mathematics. To really appreciate the inner beauty of Standard Model or supersymmetry, one must get to grips with the underlying mathematics. However, this article is written for the general reader who wishes to gain a basic understanding of some of the recent breakthroughs in particle physics without being familiar with the mathematics. Is this really possible? Yes, although I have to admit that popular expositions may be enjoyable, but without the mathematics, readers may only gain a cursory understanding of the subject. Even then the effort is worthwhile and I would call it a success if this article kindles further interest in someone in this fascinating area.

The reader, who in my view, would benefit the most from this article is a person possessing a curious and adaptable mind, not necessarily someone with a background in physics, although some exposure in undergraduate physics will definitely help, but somebody looking to be told an engaging and intellectually stimulating story, but who will not feel patronized if a few difficult ideas are explained to make a point. My goal is to tell the story of elementary particles. In most cases their existence was predicted by brilliant theoretical ideas, some of which were verified decades later by groundbreaking experiments (a great example is the Higgs boson which was theoretically predicted half a century ago and finally discovered at CERN to such aplomb), while others are still awaiting confirmation in future experimental searches. I have attempted to present a slice of that story by largely avoiding its more mathematical side. The choice of topics represents my own preferences and prejudices. The focus is the current state of the Standard Model of particle physics and on the attempts to extend it to explain the ubiquitous dark matter in our Universe. In doing so, I have often skipped some of the standard topics in order to stay the course.

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